Deep Beam transverse reinforcing development

[said the noob]

Hi All,

regarding transverse (minimum orthogonal reinforcing along each face of deep beam) reinforcing do we need to develop the horizontal reinforcing into the supports similar to tension ties? and for the vertical direction do we need to have stirrups? or would hooking them at the bottom/top suffice? also do they need to be developed at all?

I did some research and was reading this article, where if the shear span to depth ratio (a/d or a/z) is below 0.5 pure strut action can be expected, where as if the ration is between 0.5 to 2 then you would expect some transfer of loads by strut action and the other by stirrup action, the equation is in the pdf I attached. V (taken by stirrups) = Vf*(2*a/z - 1)/3, rest is transferred by strut action.

thanks all.

 

[KootK]

To an extent, the answer to your questions will depend on the worldwide location of your project. Is it in the US? I will assume so.

do we need to develop the horizontal reinforcing into the supports similar to tension ties?

When last I checked in on the north american codes, the intent of this rebar was to limit the extent of crack development around your compression struts. As such, any rebar used for this purpose needs to be developed outside of the compression field for the strut. Given that you hardest working struts are likely adjacent to your supports, I think that it's generally good practice to terminate your horizontal bars with hooks or some other kind of anchorage device. That said, I don't believe that you need to strictly develop the horizontal bars beyond the inside face of your supports/strut as you do with your flexural tension rebar.

Outside of north america, some codes have requirements for the lateral confinement of compression strut by reinforcing which creates a much more demanding situation that may lead to the use of u-bars at the beam ends etc.

and for the vertical direction do we need to have stirrups? or would hooking them at the bottom/top suffice? also do they need to be developed at all?

Since the vertical bars serve the same purpose as the horizontal bars, I would say that they do need to be developed for the same reason that the horizontal bars do. However, I do feel that hooks will suffice in this application and that stirrups are generally not required.

Basically, if your particular situation requires you to have stirrups for shear resistance, then those reinforcing pieces need to be detailed as stirrups. Otherwise, they probably don't.